US8305088B2 - Process and device for differentiating objects influencing an electromagnetic alternating field, in particular metal objects - Google Patents

Process and device for differentiating objects influencing an electromagnetic alternating field, in particular metal objects Download PDF

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US8305088B2
US8305088B2 US12/528,131 US52813108A US8305088B2 US 8305088 B2 US8305088 B2 US 8305088B2 US 52813108 A US52813108 A US 52813108A US 8305088 B2 US8305088 B2 US 8305088B2
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coil
window
current
coil current
comparator
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US20100164512A1 (en
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Michael Kiss
Bernhard Kohla
Bernd Graze
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EVK di Kerschhaggl GmbH
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EVK di Kerschhaggl GmbH
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
    • G01V3/101—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
    • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
    • B07C5/34—Sorting according to other particular properties
    • B07C5/344—Sorting according to other particular properties according to electric or electromagnetic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
    • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
    • B07C5/36—Sorting apparatus characterised by the means used for distribution
    • B07C5/363—Sorting apparatus characterised by the means used for distribution by means of air
    • B07C5/365—Sorting apparatus characterised by the means used for distribution by means of air using a single separation means
    • B07C5/366—Sorting apparatus characterised by the means used for distribution by means of air using a single separation means during free fall of the articles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/12—Measuring magnetic properties of articles or specimens of solids or fluids

Definitions

  • the invention relates to a process and a device for differentiating objects influencing an electromagnetic alternating field, in particular metal objects, using a coil arranged on a conveying route on which a material stream is moved in one direction at a predetermined speed, wherein the material stream can comprise conductive and/or ferromagnetic objects, according to the preambles of claims 1 and 12 .
  • the invention comprises a sorting plant for sorting objects from a material stream.
  • a temporally variable current I p flows through a coil S, an electromagnetic field H p builds up around said coil (see FIG. 1 ).
  • an electroconductive object O is located close to the coil, eddy currents I w are induced on the surface thereof and in layers near to the surface, based on the principle of electromagnetic induction. The current density thereby decreases as the depth increases.
  • the eddy currents I w in turn result in an electromagnetic secondary field H s , which is inverse to the primary field H p and thus weakens it. This effect is also referred to as the eddy current effect and is illustrated in FIG. 1 .
  • L S and R S are the series-connected components of an equivalent electric circuit diagram for describing the coil impedance Z S of the coil S.
  • Z S R S +j ⁇ L S .
  • eddy currents depend, on the one hand, on object properties such as the conductivity ⁇ and the relative magnetic permeability ⁇ r and hence on physical material properties, but also on the surface condition and homogeneity in the eddy current range such as the size and shape of the object and, on the other hand, also on the excitation (magnetic primary field strength H p and frequency) and the distance between objects.
  • eddy currents are induced in conductive materials by excitation coils, whereby the primary field is influenced by the resulting magnetic field.
  • This influence leads, on the one hand, to a change in the impedance of the excitation coil, which can be measured (parametric principle), on the other hand, however, the induced voltage in an additional secondary coil changes, too (transformational principle).
  • the excitation of the excitation coil with sinusoidal current is most common (single frequency method). In doing so, the coil is normally a component of an oscillating circuit, in most cases of a serial oscillating circuit. The current and voltages within the circuit change if a conductive object enters the effective range of the coil field.
  • the measurands can be measured either absolutely (absolute arrangement) or as differential signals to a reference sensor (differential arrangement).
  • the excitation of the magnetizing coil can also occur with pulsed currents (pulse induction method).
  • a sorting plant for sorting metallic particles is known, by means of which it ought to be possible to determine which materials possess metal particles.
  • Said plant consists of a detector comprising single probes in an array arrangement with a high spatial resolution.
  • the particles pass through a magnetic alternating field in a frequency range from 0.1 MHz to 1.0 MHz. Eddy currents which reduce the magnetic field develop in the metallic particles. Those changes in the magnetic field are detected by magneto-resistive sensors and transformed into electronic signals which are analyzed.
  • the sensitivity of this detector and the signal progression produced for this purpose are not sufficient for reliably sorting out, e.g., nonferrous metals between themselves.
  • said detector is relatively expensive.
  • a device and a process by means of which it is possible to sort out metals of different colours, i.e., nonferrous metals, between themselves is indicated and described in DE 100 03 562 A1.
  • a differentiation between the nonferrous metals becomes possible only by an optical sensor which is designed as a camera, whereby metal fragments have to be illuminated. Different air nozzles which are able to sort a bulk material stream in free fall are provided for sorting out.
  • a second detector designed as a metal detector is actually also arranged, but said detector is unable to distinguish between different nonferrous metals.
  • the metal detector is only able to distinguish between ferrous metals and nonferrous metals. In practice, it is therefore usable only in combination with the optical sensor.
  • the optical sensor differentiates metals only according to their appearance, but not according to their electromagnetic properties.
  • Processes are also known in which an evaporation of materials to be separated is effected with a laser or a radioactive irradiation of those materials is performed. However, those processes are relatively expensive.
  • the signal evaluation with single frequency methods is usually carried out by evaluating the peak value (“amplitude”) and/or the phase shift (“phase”) of the sinusoidal coil current toward the excitation potential of the coil, which excitation potential is also sinusoidal.
  • Rectifier circuits with a subsequent maximum value storage, scanning-holding elements or synchronous rectifiers are generally used for the “amplitude measurement”.
  • Phase-sensitive rectifiers are routinely used for measuring the phase shift (see Austrian Patent AT 501669 or Tietze, U., Schenk, Ch.: “Halbleiter-Scenstechnik”, 11 th newly revised edition (1899), p. 1058, 1212-1218).
  • the present invention is thus based on the problem of providing a process and a device for differentiating objects influencing an electromagnetic alternating field, in particular metal objects, which allow a quick and precise distinction between the above-mentioned objects in a material stream, which involves a small expenditure of hardware. Furthermore, influences of the size, thickness and shape of the objects to be differentiated on the differentiation process are to be minimized.
  • the device is supposed to be simple, sturdy and fail-safe and to allow the recovery of amplitude and phase signals in an extremely efficient manner with an analog-to-digital conversion taking place at the same time so that advantages with regard to rapidness, costs and simple construction will ensue in comparison with the otherwise customary arrangements comprising a synchronous rectifier, phase discriminator and low-pass filter, as described, e.g., in AT 501669.
  • the present invention solves the problem posed by means of a process for differentiating objects influencing an electromagnetic alternating field having the features of claim 1 as well as by means of a device for differentiating objects influencing an electromagnetic alternating field having the features of claim 12 .
  • Advantageous embodiments of the invention result from the subclaims.
  • the invention comprises a sorting plant with at least one device according to the invention for differentiating objects influencing an electromagnetic alternating field.
  • the comparator window i.e., the values of the inlet point and the outlet point of the window of the window comparator, are arranged symmetrically to a signal centre line, in particular zero line, of the coil current, linear ratios for calculating the gradient are obtained in said range, which simplify the calculation.
  • At least one peak value determined in a discrete measuring phase is preferably compared to corresponding peak values of reference samples for determining the material of the object.
  • At least one measuring phase near a maximum angle of phase difference, which occurs when the object comes closest to the coil, is selected, wherein, however, the distance between the measuring phase angle and the maximum angle of phase difference is preferably chosen to be at least so large that it is achieved also with the smallest objects occurring in the material stream.
  • a further advantage of the invention is that the moment of achieving the measuring phase angle with a known speed of the material stream can be used as a reference moment for discharging the object from the material stream.
  • the moment of achieving the maximum angle of phase difference with a known speed of the material stream can be used as a reference moment for discharging the object from the material stream.
  • the respective locus curve is received point by point for different phase angles and used for evaluation via comparison with reference locus curves.
  • a standardization can be provided by, first of all, determining the offset phase from the excitation potential distribution and the current profile of the coil in a condition which is unaffected by objects and subsequently relating the measuring phase angles of the current profiles to the offset phase.
  • the invention operates excellently at an excitation or measuring frequency f M , respectively, ranging between 1 kHz and 1 MHz, preferably between 5 and 100 kHz and most preferably between 10 and 50 kHz.
  • the coil diameter should be chosen to be smaller than an average diameter of the objects to be differentiated.
  • FIG. 1 shows the principle of the effects of an eddy current effect and a ferromagnetic effect in an electromagnetic alternating field produced by a coil
  • FIG. 2 shows locus curves and selected phasor diagrams from which the changes in impedance result which have been caused in a coil by an electroconductive and/or ferromagnetic object;
  • FIG. 3 shows voltage and current diagrams for illustrating the signal evaluation process according to the invention
  • FIG. 4 shows a schematic block diagram of an embodiment of a device according to the invention for differentiating objects influencing an electromagnetic alternating field
  • FIG. 5 shows a signal diagram of the output signals of the comparators used in the device of FIG. 4 ;
  • FIG. 6 shows a schematic illustration of a sorting plant according to the invention.
  • the excitation coil S is connected with a capacitor C into an oscillating circuit, namely in this example by a series connection of the excitation coil S and the capacitor C into a serial oscillating circuit.
  • Said oscillating circuit is loaded with a sinusoidal alternating voltage u e (t) of a constant amplitude and frequency, preferably its natural frequency, so that a current i 0 (t) flows through the coil S and hence through the serial oscillating circuit, which current is phase shifted by an offset phase angle ⁇ os relative to the excitation potential.
  • the result is a material characteristic progression of the changes in the amount and phase of the coil current depending on the x-position of the object O relative to the coil S.
  • FIG. 2 shows the above-mentioned local curve A 1 as well as a second local curve A 2 for a second object in the complex number plane, with the second object consisting of a material Mat 2 which differs in its electrical conductivity and its ferromagnetic properties, respectively, from a material Mat 1 from which the first object O is formed, for which the first local curve A 1 has been received.
  • phase shift ⁇ (x) is positive if the ferromagnetic effect is predominant ( ⁇ r >>1, iron etc.), but is negative if the eddy current effect is predominant ( ⁇ r ⁇ 1, nonferrous metals etc.). If ⁇ r >1 (e.g. 10, stainless steels etc.), both positive and negative values may occur for ⁇ (x).
  • the position vector A 1 ( x ) moves back from the reversal point A 1 ( ⁇ max ) of the locus curve A 1 in order to, ideally, reach the starting point A 1 ( ⁇ os ) of the locus curve A 1 again, with a large distance between the objects (x ⁇ + ⁇ ).
  • the moment of the occurrence of said maximum angle of phase difference ⁇ max can also be used as a reference for the discharge of objects from the material stream 2 in the sorting plant 1 , since the speed v of the material stream 2 is known.
  • the amplitudes A 1 ( ⁇ M ) and A 2 ( ⁇ M ), respectively, are indicators for the material Mat 1 or Mat 2 , respectively, of the respective object O.
  • the difference between the amplitudes A 1 ( ⁇ M ) and A 2 ( ⁇ M ) and hence the sensitivity of the measurement are the greater, the closer to the maximum angle of phase difference ⁇ max the measuring phase angle ⁇ M is chosen to be located.
  • the maximum angle of phase difference ⁇ max depends, among other things, on the size of the object O, the measuring phase angle ⁇ M must not be chosen to be too large in practice, since otherwise it might possibly not be achieved with small objects O.
  • the predetermined measuring phase angle ⁇ M is possibly achieved already with a partial covering of the coil S by the object O, i.e., if
  • the shapes of the locus curves A 1 , A 2 depend, among other things, on the following influencing variables:
  • the measuring frequency f M is kept constant, wherein a value between 1 kHz and 1 MHz, preferably between 5 and 100 kHz and most preferably between 10 and 50 kHz, has stood the test.
  • the optimization of the frequency leads to the fact that the penetration depth to be expected, on the one hand, minimizes the influences of the surface condition for the materials to be selected as much as possible, while, on the other hand, however, sufficiently thin objects are safely identified (the influence of thickness is minimized).
  • the primary field strength H p should be constant and as large as possible.
  • the coil diameter d is optimized such that the required axial object distance z from the coil is achieved, but influences of the size and shape of the object are minimized. In order to achieve this, it is suggested that a coil diameter smaller than an average diameter of the objects to be differentiated be chosen, whereas, however, it must be considered that the sensitivity of the coil decreases with a smaller coil diameter.
  • the coil shape is optimized empirically with support by the Finite Element Method (FEM).
  • FEM Finite Element Method
  • the axial object distance from the coil is kept as constant as possible.
  • Morphological object influencing variables in particular influences of the size, thickness, volume and shape of the objects, can be minimized by the measuring method according to the invention described below, influences of the surface condition of the objects are minimized for a wide object spectrum by structural measures (coil shape).
  • the device according to the invention has turned out to be very interference resistant.
  • the signal evaluation process according to the invention is now described on the basis of the voltage and current diagrams of FIG. 3 . This is subsequently followed by a description of an implementation of said process in a device according to the invention for differentiating objects influencing an electromagnetic alternating field.
  • the signal evaluation is based on an extremely efficient method in which the locus curve is determined point by point. In the most simple case, only one point of the locus curve needs to be determined and evaluated by specifying a discrete measuring phase ⁇ M and calculating the amount (amplitude) Î M of the current i M (t) in an interpolating manner upon reaching said measuring phase ⁇ M .
  • the material of the object O can be inferred from the pair of values, measuring phase ⁇ M and amount Î M , via comparison with reference values.
  • the excitation frequency f M of the magnetizing coil S dictates the sampling frequency (one measurement per period), as determined by the system.
  • the excitation frequency f M is thereby kept constant.
  • the zero crossing p 2 of the current i 0 (t) and hence the offset phase ⁇ os of the serial oscillating circuit are calculated from the excitation potential distribution u e (t) and the current profile i 0 (t) of the uncovered coil S or the uncovered serial oscillating circuit, respectively.
  • the zero crossings of the excitation potential u e (t) are indicated by reference character NL.
  • said offset phase ⁇ os may be assumed to be 0°. If an object O now enters the range of influence of the coil S, the phase ⁇ (x) changes depending on the x-position of the object O and hence also the current profile changes.
  • the current profile i M (t) illustrated in FIG. 3 adjusts itself.
  • the determination of the measuring phase angle ⁇ M is performed by measuring the zero crossing p 5 of the current profile i M (t) with the aid of a zero crossing detector (a current or voltage comparator, respectively) and a digital counter with a constant counting frequency. Since the excitation frequency (measuring frequency) f M is known, the measuring phase angle ⁇ M can be calculated from the time between the two zero crossings p 2 and p 5 , respectively.
  • the amounts (in the present specification also referred to as amplitudes and peak values, respectively) of the current profiles i 0 (t) and i M (t), respectively, are calculated with the aid of a window comparator symmetrical to a signal centre line (here to the zero line) and having a constant window width ⁇ i by measuring the gradients of the sinusoidal current profiles i 0 (t) and i M (t), respectively, which have a known frequency and have been linearized in the zero crossing.
  • the inlet point p 1 into the comparator window and the outlet point p 3 therefrom are measured for the current profile i 0 (t) by means of the window comparator and the time ⁇ t 0 between the window inlet point p 1 and the window outlet point p 3 is detected by means of a timer, which is implemented, e.g., as a digital counter of a constant counting frequency. Due to the linear progression of the sinusoidal current profile i 0 (t) between points p 1 and p 3 , the gradient of the current profile i 0 (t) in the zero crossing p 2 can be calculated from the window width ⁇ i of the window comparator and the time ⁇ t 0 .
  • the gradients and phase shifts are sufficient for a linear equation.
  • a respective pair of values, amplitude and phase shift of the current profiles i 0 ( t ) and i M (t), can thus be calculated easily from the pairs of counts obtained, whereby the associated locus curve A 1 is generated point by point by periodically detecting those pairs of values for different phase angles ⁇ (x).
  • the peak value Î can be calculated for sinusoidal currents by
  • I ⁇ 1 2 ⁇ ⁇ ⁇ f ⁇ d i d t in the current zero crossing.
  • the frequency of the sinusoidal excitation potential u e (t) and hence also the frequency f M of the evaluated coil current i 0 (t) or i M (t), respectively, is constant (linear system)
  • a direct correlation between the peak values Î 0 and Î M , respectively, of the coil currents i 0 (t) and i M (t), respectively, and the amount of the gradient ⁇ i/ ⁇ t 0 or ⁇ i/ ⁇ t M , respectively, of the tangent arises in the zero crossing.
  • the differential quotient di/dt can be replaced by the difference quotient
  • the peak value Î 0 has been standardized to 100% and thus corresponds to the amplitude of the position vector A 1 ( ⁇ os ) in the locus curve diagram of FIG. 2 .
  • the evaluation can be further simplified by using the window inlet points p 1 , p 4 or the window outlet points p 3 , p 6 instead of the current zero crossings p 2 , p 5 for the phase measurement and by dispensing with the approximation (window current ⁇ i ⁇ peak value of the current amplitude Î) and by evaluating the counts of the digital counter directly (without conversion into amplitude and phase values, respectively).
  • window current ⁇ i ⁇ peak value of the current amplitude Î the count of the digital counter directly (without conversion into amplitude and phase values, respectively).
  • the type of metal (electrical conductivity, relative magnetic permeability) can be determined very reliably for objects of various shapes, sizes and thicknesses in a wide range.
  • FIG. 4 shows a block diagram of a device 10 according to the invention for differentiating objects influencing an electromagnetic alternating field, in which the differentiation method according to the invention is implemented with some simplifications.
  • an excitation coil S is serially connected with a switchable capacitance C into a serial oscillating circuit.
  • the serial oscillating circuit is loaded with a sinusoidal alternating voltage u e (t) of a constant amplitude and frequency, preferably its natural frequency, by a FET 11 controlled by a DAC 12 so that a sinusoidal current i 0 (t) flows through the coil S and hence through the serial oscillating circuit, which current is phase shifted by an offset phase angle ⁇ os relative to the excitation potential u e (t).
  • the capacitance C is configured to be switchable in order to be able to adjust the offset phase angle ⁇ os empirically.
  • the frequency f M of the excitation potential u e (t) was determined to be 13 kHz.
  • a sine wave generator comprising an amplifier might also be used.
  • the inductance of the coil S and hence also the phase angle between the excitation potential u e (t) and the current profile through the coil will change.
  • the current profile i M (t) occurs at a defined measuring phase angle ⁇ M .
  • the current through the serial oscillating circuit is converted into a voltage signal u M (t) which is supplied to the inputs of two comparators 15 , 16 whose reference voltages are determined to be ⁇ Vref and +Vref.
  • the comparators 15 and 16 form a window comparator whose window width defined from the difference between the reference voltages +Vref and ⁇ Vref corresponds to the window width ⁇ i of the signal diagram of FIG. 3 .
  • a further comparator 14 is supplied with the excitation potential u e (t), its reference voltage is determined to be 0V so that it covers the zero crossing NL of the excitation potential u e (t).
  • the output signal K 1 of the comparator 14 depending on the excitation potential u e (t) is illustrated in the signal diagram of FIG. 5 .
  • the reference voltages ⁇ Vref and +Vref of the two comparators 15 , 16 as well as the output signal K 2 of the comparator 15 and the output signal K 3 of the comparator 16 are illustrated in the signal diagram of FIG. 5 .
  • the comparator 14 starts a first counter 18 and a second counter 19 at the zero crossing NL of the excitation potential U e (t). Both counters 18 , 19 are negatively flank-triggered.
  • the comparator 15 stops the second counter 19 at the instant p 4 when the input signal u M (t) exceeds its reference voltage value ⁇ Vref, i.e., enters into the comparator window.
  • the comparator 16 stops the first counter 18 at the instant p 6 when the input signal exceeds its reference voltage value +Vref, i.e., leaves the comparator window.
  • the two counters 18 , 19 are designed as digital counters with a constant counting frequency so that the time difference ⁇ t M can be derived from the difference between the two counts, in this connection, confer FIG. 3 .
  • the two counters 18 , 19 are integrated in a microcontroller 17 .
  • the gradient of the signal u M (t) in the zero crossing p 5 can be determined from the time difference ⁇ t M and the known frequency of the signal u M (t) and the amplitude of the signal u M (t) can be calculated from the gradient, as has been described above on the basis of the formulae.
  • the comparator 15 could start a counter ( 18 or 19 ) and the comparator 16 could stop the counter. From the count, the length of time ⁇ t M is directly derivable which the coil current i M (t) needs in order to pass through the comparator window ⁇ i, from which, in turn, the peak value can be calculated.
  • phase between the signals u e (t) and u M (t) is derived with a small, but constant error from the difference between the instants NL and p 4 .
  • the amplitude of the signal u M (t) is not calculated directly from the above-indicated formulae, but the counted measurand of the second counter 19 is used as an index of a reference value table which is stored in an EEPROM 21 and, for each index value Ref — 1-Ref — 5, possesses a reference threshold value Lim — 1-Lim — 5 associated therewith, with which the counted measurand of the first counter 18 is compared in a digital comparator 23 .
  • a classification and object-length determination unit 24 infers the material of the object from exceeding or falling below the reference threshold value Lim — 1-Lim — 5 used in each case.
  • the counts of the first and second counters 18 , 19 are thus evaluated directly, i.e., without previous conversion into amplitude and phase values, respectively.
  • the reference value table By providing the reference value table, the fact is taken into account that different optimum points for measuring exist for different decisions regarding materials (VA-NE, Al—Cu, . . . ). Since each object approaches the coil, a new count in the second counter 19 and hence a new reference and limiting value exist in each sample period.
  • the microcontroller 17 furthermore comprises a timer 20 and a RAM 22 , wherein the metered measurands of the timer 20 control the reading of associated tabular values from the RAM 22 into the DAC, which values provide for the generation of the sinusoidal voltage u e (t).
  • a sorting plant 1 according to the invention is illustrated schematically. It comprises a conveyor belt 3 on which a material stream 2 moves at a constant speed v in which objects O are contained which are supposed to be identified and sorted out based on their conductivity and/or ferromagnetic properties.
  • a device 10 according to the invention for differentiating the objects O is arranged below the conveyor belt 3 .
  • the coil S of an oscillating circuit of the device 10 is arranged such that its coil axis SA is at right angles to the conveying direction (x-direction) of the material stream 2 . Furthermore, the coil S is at a distance z from the material stream 2 —measured in the direction of the coil axis SA.
  • the diameter d of the coil S is dimensioned such that it is smaller than an average diameter D of the objects O to be differentiated. If the objects O move in the x-direction across the central point of the coil (coil axis SA), a material characteristic progression of the changes in the amount and phase of the coil current depending on the x-position of the object O relative to the coil S sets in, which is evaluated in the device 10 . Depending on the result of the evaluation, the device 10 activates an object discharging unit 4 , for example, an air nozzle, which discharges the objects O from the material stream 2 . In the illustrated exemplary embodiment, the sorted material stream 2 reaches a container 5 .
  • an object discharging unit 4 for example, an air nozzle
  • a plurality of coils are arranged across the width of the conveyor belt 3 , with the intervals between coils being chosen such that no object O can pass between the coverages of the coils without being noticed.
  • a conveyor belt 3 for example, a slide may also be provided.

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US12/528,131 2007-02-23 2008-02-22 Process and device for differentiating objects influencing an electromagnetic alternating field, in particular metal objects Expired - Fee Related US8305088B2 (en)

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Application Number Priority Date Filing Date Title
AT0029407A AT504527B1 (de) 2007-02-23 2007-02-23 Verfahren und vorrichtung zum unterscheiden von ein elektromagnetisches wechselfeld beeinflussenden objekten, insbesondere metallobjekten
ATA294/2007 2007-02-23
PCT/AT2008/000059 WO2008101270A1 (de) 2007-02-23 2008-02-22 Verfahren und vorrichtung zum unterscheiden von ein elektromagnetisches wechselfeld beeinflussenden objekten, insbesondere metallobjekten

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US10551215B2 (en) 2015-06-11 2020-02-04 Analog Devices Global Unlimited Company Systems, circuits and methods for determining a position of a movable object

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